Abstract
In the third paper from the COOL–LAMPS Collaboration, we report the discovery of COOL J0542-2125, a gravitationally lensed quasar at
z
= 1.84, observed as three images due to an intervening ...massive galaxy cluster at
z
= 0.61. The lensed quasar images were identified in a search for lens systems in recent public optical imaging data and have separations on the sky up to 25.″9, wider than any previously known lensed quasar. The galaxy cluster acting as a strong lens appears to be in the process of merging, with two subclusters separated by ∼1 Mpc in the plane of the sky, and their central galaxies showing a radial velocity difference of ∼1000 km s
−1
. Both cluster cores show strongly lensed images of an assortment of background sources, as does the region between them. A preliminary strong lens model implies masses of
M
<
250
k
p
c
=
1.79
−
0.01
+
0.16
×
10
14
M
⊙
and
M
<
250
k
p
c
=
1.48
−
0.10
+
0.04
×
10
14
M
⊙
for the east and west subclusters, respectively. This line of sight is also coincident with an ROSAT ALL-sky Survey source, centered between the two confirmed cluster halos reminiscent of other major cluster-scale mergers. Archival and new follow-up imaging show flux variability in the quasar images of up to 0.4 mag within ∼1 yr, and new multicolor imaging data reveal a 2
σ
detection of the underlying quasar host. A lens system with this configuration offers rare opportunities for a range of future studies of both the lensed quasar and its host and the foreground cluster merger causing the lensing.
Abstract
We report the discovery of COOL J0335−1927, a quasar at
z
= 3.27 lensed into three images with a maximum separation of 23.″3 by a galaxy cluster at
z
= 0.4178. To date, this is the highest ...redshift wide-separation lensed quasar known. In addition, COOL J0335−1927 shows several strong intervening absorbers visible in the spectra of all three quasar images with varying equivalent widths. The quasar also shows mini-broad line absorption. We construct a parametric strong gravitational lens model using ground-based imaging, constrained by the redshift and positions of the quasar images as well as the positions of three other multiply imaged background galaxies. Using our best-fit lens model, we calculate the predicted time delays between the three quasar images to be Δ
t
AB
=
499
−
146
+
141
(stat) and Δ
t
AC
=
−
127
−
17
+
83
(stat) days. Folding in systematic uncertainties, the model-predicted time delays are within the ranges 240 < Δ
t
AB
< 700 and −300 < Δ
t
AC
< −30. We also present
g
-band photometry from archival Dark Energy Camera Legacy Survey and Pan-STARRS imaging, and new multi-epoch observations obtained between 2022 September 18 UT and 2023 February 22 UT, which demonstrate significant variability in the quasar and will eventually enable the measurement of the time delay between the three quasar images. The currently available light curves are consistent with the model-predicted time delays. This is the fifth paper from the COOL-LAMPS collaboration.
Wide-separation lensed quasars (WSLQs) are a rare class of strongly lensed
quasars, magnified by foreground massive galaxy clusters, with typically large
magnifications of the multiple quasar images. ...They are a relatively unexplored
opportunity for detailed study of quasar host galaxies. The current small
sample of known WSLQs has a median redshift of $z\approx 2.1$, larger than most
other samples of quasar host galaxies studied to date. Here, we derive precise
constraints on the properties of six WSLQs and their host galaxies, using
parametric surface brightness fitting, measurements of quasar emission lines,
and stellar population synthesis of host galaxies in six WSLQ systems. Our
results, with significant uncertainty, indicate that these six hosts are a
mixture of star-forming and quiescent galaxies. To probe for co-evolution
between AGNs and host galaxies, we model the offset from the `local' ($z=0$)
$M_{\rm{BH}}\unicode{x2013}M_\star$ relation as a simple power-law in redshift.
Accounting for selection effects, a WSLQ-based model for evolution in the
$M_{\rm{BH}}\unicode{x2013}M_\star$ relation has a power-law index of
$\gamma_M=-0.42\pm0.31$, consistent with no evolution. Compared to several
literature samples, which mostly probe unlensed quasars at $z<2$, the WSLQ
sample shows less evolution from the local relation, at $\sim 4\sigma$. We find
that selection affects and choices of $M_{\rm{BH}}$ calibration are the most
important systematics in these comparisons. Given that we resolve host galaxy
flux confidently even from the ground in some instances, our work demonstrates
that WSLQs and highly magnified AGNs are exceptional systems for future
AGN$\unicode{x2013}$host co-evolution studies.
We report the discovery of COOL J0335$-$1927, a quasar at z = 3.27 lensed
into three images with a maximum separation of 23.3" by a galaxy cluster at z =
0.4178. To date this is the highest redshift ...wide-separation lensed quasar
known. In addition, COOL J0335$-$1927 shows several strong intervening
absorbers visible in the spectra of all three quasar images with varying
equivalent width. The quasar also shows mini-broad line absorption. We
construct a parametric strong gravitational lens model using ground-based
imaging, constrained by the redshift and positions of the quasar images as well
as the positions of three other multiply-imaged background galaxies. Using our
best-fit lens model, we calculate the predicted time delays between the three
quasar images to be $\Delta$t$_{AB}=$ $499^{+141}_{-146}$ (stat) and
$\Delta$t$_{AC}=$ $-127^{+83}_{-17}$ (stat) days. Folding in systematic
uncertainties, the model-predicted time delays are within the ranges $240 <
\Delta$t$_{AB} < 700$ and $-300 < \Delta$ t$_{AC} <-30$. We also present g-band
photometry from archival DECaLS and Pan-STARRS imaging, and new multi-epoch
observations obtained between September 18, 2022 UT and February 22, 2023 UT,
which demonstrate significant variability in the quasar and which will
eventually enable a measurement of the time delay between the three quasar
images. The currently available light curves are consistent with the
model-predicted time delays. This is the fifth paper from the COOL-LAMPS
collaboration.
We compute parametric measurements of the Einstein-radius-enclosed total mass for 177 cluster-scale strong gravitational lenses identified by the ChicagO Optically-selected Lenses Located At the ...Margins of Public Surveys (COOL-LAMPS) collaboration with lens redshifts ranging from \(0.2 \lessapprox z \lessapprox 1.0\) using only two measured parameters in each lensing system: the Einstein radius, and the brightest-cluster-galaxy (BCG) redshift. We then constrain the Einstein-radius-enclosed luminosity and stellar mass by fitting parametric spectral energy distributions (SEDs) with aperture photometry from the Dark Energy Camera Legacy Survey (DECaLS) in the \(g\), \(r\), and \(z\)-band Dark Energy Camera (DECam) filters. We find that the BCG redshift, enclosed total mass, and enclosed luminosity are strongly correlated and well described by a planar relationship in 3D space. We also find that the enclosed total mass and stellar mass are correlated with a logarithmic slope of \(0.443\pm0.035\), and the enclosed total mass and stellar-to-total mass fraction are correlated with a logarithmic slope of \(-0.563\pm0.035\). The correlations described here can be used to validate strong lensing candidates in upcoming imaging surveys -- such as Rubin/Legacy Survey of Space and Time (LSST) -- in which an algorithmic treatment of lensing systems will be needed due to the sheer volume of data these surveys will produce.
In the third paper from the COOL-LAMPS Collaboration, we report the discovery of COOL J0542-2125, a gravitationally lensed quasar at \(z=1.84\), observed as three images due to an intervening massive ...galaxy cluster at \(z=0.61\). The lensed quasar images were identified in a search for lens systems in recent public optical imaging data and have separations on the sky up to 25".9, wider than any previously known lensed quasar. The galaxy cluster acting as a strong lens appears to be in the process of merging, with two sub-clusters separated by \(\sim 1\) Mpc in the plane of the sky, and their central galaxies showing a radial velocity difference of \(\sim 1000\) km/s. Both cluster cores show strongly lensed images of an assortment of background sources, as does the region between them. A preliminary strong lens model implies masses of \(M(<250\ \rm{kpc}) = 1.79^{+0.16} _{-0.01} \times 10^{14} M_{\odot}\) and \(M(<250\ \rm{kpc}) = 1.48^{+0.04}_{-0.10} \times 10^{14} M_{\odot}\) for the East and West sub-clusters, respectively. This line of sight is also coincident with a ROSAT ALL-sky Survey source, centered between the two confirmed cluster halos reminiscent of other major cluster-scale mergers.
We report the discovery of COOL J0335\(-\)1927, a quasar at z = 3.27 lensed into three images with a maximum separation of 23.3" by a galaxy cluster at z = 0.4178. To date this is the highest ...redshift wide-separation lensed quasar known. In addition, COOL J0335\(-\)1927 shows several strong intervening absorbers visible in the spectra of all three quasar images with varying equivalent width. The quasar also shows mini-broad line absorption. We construct a parametric strong gravitational lens model using ground-based imaging, constrained by the redshift and positions of the quasar images as well as the positions of three other multiply-imaged background galaxies. Using our best-fit lens model, we calculate the predicted time delays between the three quasar images to be \(\Delta\)t\(_{AB}=\) \(499^{+141}_{-146}\) (stat) and \(\Delta\)t\(_{AC}=\) \(-127^{+83}_{-17}\) (stat) days. Folding in systematic uncertainties, the model-predicted time delays are within the ranges \(240 < \Delta\)t\(_{AB} < 700\) and \(-300 < \Delta\) t\(_{AC} <-30\). We also present g-band photometry from archival DECaLS and Pan-STARRS imaging, and new multi-epoch observations obtained between September 18, 2022 UT and February 22, 2023 UT, which demonstrate significant variability in the quasar and which will eventually enable a measurement of the time delay between the three quasar images. The currently available light curves are consistent with the model-predicted time delays. This is the fifth paper from the COOL-LAMPS collaboration.
Wide-separation lensed quasars (WSLQs) are a rare class of strongly lensed quasars, magnified by foreground massive galaxy clusters, with typically large magnifications of the multiple quasar images. ...They are a relatively unexplored opportunity for detailed study of quasar host galaxies. The current small sample of known WSLQs has a median redshift of \(z\approx 2.1\), larger than most other samples of quasar host galaxies studied to date. Here, we derive precise constraints on the properties of six WSLQs and their host galaxies, using parametric surface brightness fitting, measurements of quasar emission lines, and stellar population synthesis of host galaxies in six WSLQ systems. Our results, with significant uncertainty, indicate that these six hosts are a mixture of star-forming and quiescent galaxies. To probe for co-evolution between AGNs and host galaxies, we model the offset from the `local' (\(z=0\)) \(M_{\rm{BH}}\unicode{x2013}M_\star\) relation as a simple power-law in redshift. Accounting for selection effects, a WSLQ-based model for evolution in the \(M_{\rm{BH}}\unicode{x2013}M_\star\) relation has a power-law index of \(\gamma_M=-0.42\pm0.31\), consistent with no evolution. Compared to several literature samples, which mostly probe unlensed quasars at \(z<2\), the WSLQ sample shows less evolution from the local relation, at \(\sim 4\sigma\). We find that selection affects and choices of \(M_{\rm{BH}}\) calibration are the most important systematics in these comparisons. Given that we resolve host galaxy flux confidently even from the ground in some instances, our work demonstrates that WSLQs and highly magnified AGNs are exceptional systems for future AGN\(\unicode{x2013}\)host co-evolution studies.
